JPH0144769B2 - - Google Patents

Description

[Detailed description of the invention]

Purpose of the Invention The present invention relates to a method for manufacturing a bent pipe in which a seam portion having a high-toughness weld metal portion is submerged arc welded, in which a straight pipe SAW seam welded is heated by high-frequency induction using a controlled rolled steel plate. When manufacturing bent pipes, by specifying the composition of the welded metal part and limiting the heating conditions for the straight pipes, the product can be made as is (without tempering) by being quenched while being bent. The purpose of the present invention is to provide a simple and low-cost manufacturing method for a bent pipe in which the welded metal part has excellent strength and toughness. Industrial Application Fields Manufacturing technology for bent pipes with high toughness welded metal parts. Conventional technology Mass transportation of crude oil and natural gas from underground resources harvested as raw materials and fuel for industrial use, liquids, gases, and slurries obtained by refining them, and other industrial liquids, gases, slurries, etc. other than raw materials and fuels. It is well known that a pipeline is used as a means. In order to improve the transportation efficiency of this pipeline, the pumping pressure is increased, and as a measure to install the pipeline in a cold region, the quality requirements for the steel pipe are becoming even more high tensile strength, and the requirements for low-temperature impact properties are also gradually becoming stricter. ing. By the way, fittings such as bent pipes used in pipelines, etc. are made by press-forming steel plates with performance equivalent to or better than straight pipes, then facing each other and seam welding them to form a predetermined shape. Alternatively, straight pipes are manufactured by cold or hot processing into the desired shape, and then subjected to quenching and tempering heat treatment, but from the standpoint of productivity, high-frequency heating of straight pipes is recommended. While doing so, as shown in FIG. 7, the base tube 15 is guided by guide rollers 16, 16, and its base end is clamped by a rotating arm 18 which is pivoted 17, and the rotating arm 18 is moved from the solid line position to the imaginary line position. There is a method in which the pipe is rotated to advance the bending to form the bent pipe 15a, and then rapidly cooled to produce the bent pipe. As mentioned above, a controlled draw rolling steel plate is used for the bent pipe as a fitting material for line pipes that are used in harsh environments, and the straight pipe is seam welded using SAW (submerged arc welding) and then heated by high-frequency induction to form the bent pipe. This is as shown in Figure 6, where the bent part 11 is quenched and tempered (QT), the straight pipe part 12 is only tempered, and the bent part 11 is subjected to high-frequency induction heating, water cooling, and bending. , the entire steel pipe is heated and tempered in a furnace. Problems to be Solved by the Invention However, in the conventional method as described above, the process of heating and tempering the entire steel pipe with the seam submerged arc welded in a furnace is complicated and expensive. This is a major factor in increasing costs. Therefore, omitting this tempering treatment brings a great advantage in reducing costs, but in this case, the bent parts remain hardened and the straight pipe parts remain welded, so in terms of material performance, it is better to leave them as hardened. and must be satisfied simultaneously in the as-welded state,
No technology has been obtained that satisfies this relationship, and the disadvantages described above are considered unavoidable. "Structure of the invention" Means for solving the problem (1) C: 0.02 to 0.12wt%, Si: 0.6wt% or less,
Mn: 1.20-1.60wt%, P: 0.02wt% or less,
S: 0.15wt% or less, Nb: 0.05wt% or less, Al:
0.02wt% or less, N: 0.010wt% or less, O:
Ac ₃
It is heated above a point and quenched while being bent.
A method for manufacturing a bent pipe in which a seam portion having a high toughness weld metal portion is submerged arc welded, characterized in that the product is made into a product as is after cooling. (2) C: 0.02 to 0.12wt%, Si: 0.6wt% or less,
Mn: 1.20-1.60wt%, P: 0.02wt% or less,
S: 0.15wt% or less, Nb: 0.05wt% or less, Al:
0.02wt% or less, N: 0.010wt% or less, O:
Contains 0.035wt% or less, Cu: 0.5wt% or less, Ni: 3.0wt% or less, Mo:
0.7wt% or less, V: 0.07wt% or less, Ti: 0.06wt
% or less, B: contains one or more of the following 0.0030wt% or less, and the remainder is
A high-toughness weld metal part characterized by heating a straight pipe having a weld metal part with a composition consisting of Fe and inevitable impurities to ₃ Ac points or more, quenching it while bending it, and making it into a product as it is after cooling. A method for manufacturing a bent pipe in which a seam portion having a seam portion is submerged arc welded. Function The present invention relates to a method for manufacturing a bent pipe using a pipe whose seam portion is submerged arc welded.
The composition of the weld metal part is Si: 0.6wt% or less (hereinafter simply referred to as %), Mn: 1.2% or more, P: 0.02% or less,
S: 0.015% or less, Nb: 0.05% or less, Al: 0.05%
Below, by setting N: 0.1% or less and O: 0.035% or less, the as-welded toughness is improved, and C: 0.02%.
As described above, by setting Mn to 1.6% or less and O to 0.035% or more, as-quenched toughness can be increased. C: 0.12% or less, P: 0.02% or less, S: 0.015%
By doing the following, solidification cracking can be completely eliminated. The weld metal part in the present invention is a zone having a composition formed by melting both the welding material (welding rod and flux) and the base metal steel plate by arc heat. A favorable hardening effect can be obtained by heating to Ac ₃ or higher to austenite, followed by quenching while bending, and a decrease in toughness can be avoided by setting the cooling rate to 60℃/sec or less. It will be done. Note that toughness deterioration can be effectively avoided if quenched at 110°C or lower. EXAMPLES To further explain the present invention as described above, in view of the above-mentioned actual circumstances, the present inventors have investigated the influence of various elements in order to satisfy both the high toughness performance of the welded part in as-quenched and as-welded states. As a result of a systematic study, the chemical composition of the SAW weld metal part as described above is C: 0.02 to 0.12%, Si: 0.6%.
Below, Mn: 1.20-1.60%, P: 0.02% or less, S:
0.015% or less, Nb: 0.05% or less, Al: 0.005 to 0.07
%, N: 0.010% or less, O: 0.035% or less, with the balance consisting of Fe and inevitable impurities,
And the above component composition includes Cu: 0.5% or less, Ni: 3.0%
Below, Mo: 0.7% or less, V: 0.07% or less, Ti:
Steel pipes containing one or more of the following: 0.06% or less, B: 0.0030% or less, Ac ₃ points or more, preferably
Ac It is heated to a temperature of ₃ points or more and 1100℃ or less and then quenched.When hot bending a straight pipe to make a bent pipe, bend it while heating and quenching as described above to make the desired bent pipe. As shown in FIG. 1, a bent pipe consisting of an as-quenched bent section 1 and an as-welded straight section 2 is obtained. The reasons for limiting the chemical components in the weld metal part of the present invention as described above are explained below. C is the element that has the greatest effect on as-quenched strength and toughness, and it is desirable to use a low carbon content to ensure as-quenched toughness, but the tensile strength decreases and the required strength is not reached. Since it would not be possible to satisfy the following criteria, ultra-low carbon could not be achieved, and the lower limit was set at 0.02%. Further, on the high C side, even if the strength is satisfactory, high toughness cannot be obtained, and if it exceeds 0.12%, the solidification cracking susceptibility of the weld metal increases, so this was set as the upper limit. If Si exceeds 0.6%, it will harden as welded, resulting in a significant decrease in toughness, and the desired toughness will not be obtained even as quenched, so 0.6% was set as the upper limit. Mn is based on the relationship shown in Figure 2, which is 0.03C−1.7Mn−0.04Nb−
0.015Ti−0.0009B and 0.03C−1.2Mn−0.3Cu−
This figure shows the effect of Mn content on the strength and toughness of as-welded and as-quenched SAW weld metals for base metals of 0.07V−0.01Ti, and the strength increases as the Mn content increases. However, in the region of less than 1.2%, the as-welded toughness decreases significantly, and even in the as-quenched state, a decrease in toughness is observed. In other words, in order to simultaneously satisfy high strength and as-welded and as-quenched toughness, it is necessary to increase the toughness to 1.2% or more, and especially in the 1.4 to 1.5% range, the as-welded and as-quenched toughness overlap. Good toughness was obtained. However, if Mn is excessively increased, high toughness can be obtained when welded, but when quenched it becomes too hard and high toughness cannot be obtained.
It is necessary to set the upper limit to 1.6%. P is an element that affects the toughness and solidification cracking of the weld metal, and the smaller the content, the better, and the content should be 0.02% or less to prevent a decrease in the toughness of the weld metal and eliminate solidification cracking. . Like P, S is an element that affects the toughness and solidification cracking of weld metal, and the smaller the amount, the better.
The upper limit should be %. Nb is contained in the weld metal because it is diluted from the base metal rather than being added from the welding material, and the base metal is usually Nb.
In order to use a controlled draw rolling steel plate with a high content, it is diluted into the weld metal. However, from the standpoint of ensuring the strength and toughness of the weld metal as described above in the present invention, less is better, and the upper limit should be 0.05%. In order to deoxidize the molten metal, it is preferable to contain a trace amount of Al, and the value is 0.005% or more. However, since a large amount of Al deteriorates the toughness of the weld metal, excessive addition should be avoided, and it was limited to 0.05% or less. N is harmful to improving the toughness of weld metal,
The lower the better, the upper limit is 0.1%. O greatly affects the toughness of as-welded and as-quenched weld metals, and the smaller the amount, the higher the toughness. However, since the oxygen content of the weld metal is approximately 5 to 10 times higher than that of the base metal, reducing this oxygen content is the most important issue for improving the toughness of the weld metal. In the present invention, this is reduced to 0.035% by using a high-temperature base melting type flux.
Limited to the following. The components added as optional components to the above-mentioned basic component composition are as follows. Cu improves the strength and toughness of the as-quenched weld metal, but if it exceeds 0.5%, solidification cracking will occur in the weld metal, so this should be the upper limit. Ni is the most suitable element for obtaining high toughness in as-welded and as-quenched weld metals, so it is better to include a large amount of it; however, weld metals containing more than 3.0% Ni are susceptible to solidification cracking. This is set as the upper limit because it is dangerous. Mo is an effective element for improving the toughness of the weld metal in the as-welded state, but in the as-quenched state it is a significant hardening element and causes a decrease in toughness, so the upper limit should be 0.7% to balance these factors. . Regarding Ti, this is due to the effect on vE-46℃ of as-welded and as-quenched weld metals as shown in Figure 3 for the same base metal as in Figure 2 above, and in the area where Mn is 1.2% or more. By adding a small amount of Ti, about 0.012%, to the weld metal, remarkable high toughness can be obtained in the as-welded state. However, if the Ti content exceeds 0.06%, precipitation hardening occurs in the weld metal, resulting in a significant decrease in as-welded toughness.
0.06% or less. By adding B in combination with Ti, it improves the hardenability in as-welded condition and creates a uniform accidental ferrite.
However, if it is left as quenched, it will become too hard and the toughness will deteriorate significantly. Therefore, in the present invention, the content is set to 0.0030% or less. Although V increases the strength of as-welded and as-quenched weld metals, it cannot be said to be effective for improving toughness. However, this V is not actively added to the welding material, but is an element that enters the weld metal by diluting the base metal, and when using a base metal containing V, the weld metal contains 0.07%. Limited to the following. Next, regarding heat treatment, in the present invention
SAW weld metal with Ac of ₃ points or more, preferably Ac ₃ ~
It is heated to a temperature of 1100°C and quenched at a cooling rate of 60°C/sec or less, and the reason for this limitation is as follows. In other words, Figure 4 shows the effect of quenching temperature on the strength and toughness of weld metal.In order to quench steel, it must first be heated to a temperature of Ac ₃ or higher to form austenite, and then quenched. is common.
However, as can be understood from FIG. 4, if the quenching temperature becomes too high, the strength will increase but the toughness will deteriorate significantly, so it is preferable to quench at a temperature of 1100° C. or lower. Figure 5 shows the influence of the cooling rate when quenching at 1000℃, and it is observed that as the cooling rate increases, the strength increases and the toughness decreases. Cooling rate should be adopted. A specific structural example of the device according to the present invention will be described below. Table 1 below shows the chemical composition of the test steel plate used by the inventors.
0.04C−1.5Mn−0.3Cu−0.13Ni−0.034Nb−
It is of 0.011Ti−0.0032N.

[Table] Also, the welding conditions using a two-electrode SAW were to form a 45° groove on the inner surface of the steel plate with a thickness of 5 mm and on the outer surface with a thickness of 5.5 mm, and then Using the welding materials in Table 2, the inner surface is 1050A36V,
950A40V, 800mm/min, 1200A38V on the outside,
Welded at 1000A44V, 850mm/min.

[Table] Further, the chemical composition of the weld metal part thus obtained is as shown in Table 3 below, and is within the scope of the present invention.

[Table] After heating this weld metal to 1000℃, holding it for 1 minute, and quenching it at a cooling rate of 20℃/sec, the mechanical properties of the weld metal were investigated, and the results are shown in Table 4 below. It was like that.

[Table] In other words, it is clear that high strength and high toughness are achieved in both the as-welded and as-quenched states. "Effects of the Invention" According to the present invention as explained above, it is possible to ensure sufficient high strength and high toughness in the as-welded and as-quenched weld metal parts of a pipe whose seam part is submerged arc welded. Therefore, the invention does not require the complicated process of heating and tempering the entire steel pipe in a furnace, and it is possible to manufacture bent pipes at a preferable cost reduction, and this invention has great industrial effects. .

[Brief explanation of drawings]

The drawings show the technical content of the present invention, and Fig. 1 is an explanatory diagram of a bent pipe obtained by the method of the present invention, and Fig. 2 is an illustration of the strength and toughness of as-welded and as-quenched SAW weld metal. Figure 3 is a diagram showing the influence of Mn content on vE-46℃ in as-welded and as-quenched weld metals. Figure 4 is a chart showing the effect of quenching temperature on the strength and toughness of weld metal, Figure 5 is a chart showing the effect of cooling rate when quenching at 1000℃, and Figure 6 is a chart showing the effect of cooling rate on the strength and toughness of weld metal. FIG. 7 is an explanatory diagram of a bent tube manufactured by the tempering method, and FIG. 7 is an explanatory diagram of a conventional method of manufacturing a bent tube by high-frequency heating. However, in these drawings, 1 shows a bent part due to as-quenching, and 2 shows a straight pipe part due to as-welded.

Claims (1)

[Claims] 1 C: 0.02 to 0.12wt%, Si: 0.6wt% or less,
Mn: 1.20-1.60wt%, P: 0.02wt% or less, S:
0.15wt% or less, Nb: 0.05wt% or less, Al: 0.02wt
% or less, N: 0.010wt% or less _, O: 0.035wt% or less, and the balance is Fe and unavoidable impurities. A method for manufacturing a bent pipe in which a seam portion having a high-toughness weld metal portion is submerged arc welded, the method comprising quenching while processing and producing the product as is after cooling. 2 C: 0.02 to 0.12wt%, Si: 0.6wt% or less,
Mn: 1.20-1.60wt%, P: 0.02wt% or less, S:
0.15wt% or less, Nb: 0.05wt% or less, Al: 0.02wt
% or less, N: 0.010wt% or less, O: 0.035wt% or less, Cu: 0.5wt% or less, Ni: 3.0wt% or less, Mo:
0.7wt% or less, V: 0.07wt% or less, Ti: 0.06wt%
Below, B: contains any one or more of 0.0030wt% or less, and the balance is Fe.
A high-toughness weld metal part is produced by heating a straight pipe having a weld metal part with a composition consisting of unavoidable impurities, heating it to Ac ₃ or higher, quenching it while bending it, and making it into a product as it is after cooling. A method for manufacturing a bent pipe in which the seam portion is submerged arc welded.